Yard & Garden Line News Volume 8 Number 6                                                               May 1, 2006

Features this issue: I'm So Blue! All-America Selections for Your Minnesota Garden Tiny Reddish Clover Mites Active Now Be On the Watch For Columbine Sawfly Garden Calendar Editorial Notes

I'm So Blue!
Nancy Rose, Regional Extension Educator, Horticulture

Abies concolor Photo credit: Nancy Rose

There's something about the color blue that fascinates gardeners. We love true blue flowers like delphiniums and edging lobelia (Lobelia erinus). Blue foliage on everything from hostas to ornamental grasses to evergreens also catches our eye.

It's no wonder then that blue forms of Colorado spruce (Picea pungens f. glauca) are popular choices for landscape use. Seedlings of Picea pungens show a range of foliage color, from the typical dusty gray-green to blue-green to occasional silvery blue types. Nursery growers select out the bluest seedlings and sell them at a premium. A number of distinctly blue forms have been selected and given cultivar names including 'Fat Albert', 'Hoopsii', and 'Thompsenii'. These cultivars are propagated vegetatively by grafting.

Blue Colorado spruce can look striking or garish in the landscape, depending upon your personal taste in plants. Unfortunately, they can also often look half dead because of their susceptibility to several fungal diseases including Cytospora canker and Rhizosphaera needle cast. Trees affected by Cytospora canker show scattered branches with dead foliage all the way to the tips, plus diamond-shaped, resin-crusted cankers on branches. Symptoms of Rhizosphaera needle cast are lower branches with needles dying and dropping except on the branch tips, and eventually entirely dead branches starting near the base and moving up. These diseases commonly affect Colorado spruce in the humid, hot-summer Midwest region, but they are less of a problem in the tree's native range, the cooler, drier climate of the Rocky Mountains in Colorado, New Mexico, and Utah.

'Blue Chip' juniper Photo credit: Bailey Nurseries

If you crave some cool blue evergreen foliage in your yard but don't want a blue Colorado spruce, there are some options. If you'd still like a tree with that conical "Christmas tree" look, concolor fir (Abies concolor) may be for you. Like Colorado spruce, seedlings of concolor fir show a range of foliage color including some nice blues. You may need to browse through plants at a nursery to find one with the bluest color. Blue forms are sometimes lumped under the name Violacea Group or even as a cultivar, 'Violacea'. The concolor fir cultivar 'Argentea' (synonym 'Candicans') has distinctly silvery-blue foliage.

Another fir with bluish foliage is Rocky Mountain (or alpine) fir (Abies lasiocarpa var. arizonica). The foliage of cultivar 'Argentea' (synonym 'Glauca') has especially noticeable silver-blue color. A compact blue-foliaged cultivar is Abies lasiocarpa 'Arizonica Compacta' (syn. 'Glauca Compacta'), which forms a dense, slow-growing pyramid about 4 to 5 feet tall. As you may have noticed, these fir species and their cultivars are fraught with confusion over the proper nomenclature.

Pines are another good source of the blues. The foliage of our beautiful native Eastern white pine (Pinus strobus) naturally tends toward blue green, but the cultivar 'White Mountain' is notable for having very blue needles. The dwarf, globe-shaped cultivar 'Blue Shag' has a nice blue cast also. Blue-foliaged cultivars of other 5-needled pines include 'Extra Blue' limber pine (Pinus flexilis), blue Balkan pine (Pinus peuce 'Glauca'), and Korean pine (Pinus koraiensis) cultivars 'Glauca', 'Morris Blue', and 'Silveray'.

'Blue Star' juniper Photo credit: Nancy Rose

Scotch pine (Pinus sylvestris), a 2-needled pine, also tends to have blue-green foliage, though some individual plans are more gray-green or yellow-green. A number of cultivars of Scotch pine have been selected for having steely blue needle color. One of the most striking full-sized (40+ ft.) cultivars is 'Bonna' with its silvery blue foliage. 'Mt. Vernon' is also full-sized and has darker blue needles. The name "French Blue" is sometimes listed as a cultivar name but actually refers to seedlings grown from Pinus sylvestris populations in a specific region in France - seedlings may or may not be more blue than other seedlings of the species. Though not strongly blue, the dwarf Scotch pine cultivar 'Glauca Nana' has attractive blue-greeen foliage and slowly forms a dense 6 ft. mound.

Last but not least, junipers provide blue-loving gardeners with a number of choice cultivars. One of the richest sources is Rocky Mountain juniper (Juniperus scopulorum), a typically narrow, upright small tree (15-30 ft.) native to parts of the western U.S. and Canada. This species tolerates dry soil and is useful for hedge or accent plantings. Blue-foliaged cultivars include 'Wichita Blue', 'Blue Trail', and 'Blue Arrow'. The latter cultivar and the similar cultivar 'Skyrocket' are sometimes listed as Juniperus virginiana rather than J. scopulorum. A weeping form, 'Tolleson's Blue Weeping', makes an interesting addition to the landscape. Blue foliage also shows up in cultivars of lower-growing junipers such as creeping juniper (J. horizontalis; 'Blue Prince', 'Blue Chip', 'Wiltonii'), singleseed juniper (J. squamata 'Blue Star'), and savin juniper (J. sabina 'Blue Forest'). These junipers are attractive as groundcovers or spilling over retaining walls and terraces.

All-America Selections for Your Minnesota Garden
Nancy Rose, Regional Extension Educator - Horticulture

'Evolution salvia.

'Diamonte Coral Rose' diascia.

''Delfino' cilantro.

'Zowie! Yellow Flame' zinnia.

'Carmen' pepper.

Photo credit: All-American Selections

Each year the All-America Selections organization names a handful of new flower and vegetable varieties as the top of the crop for gardeners. The winning plants are selected from many new introductions that are grown at AAS trial sites around the country. These flowers and vegetables are judged to have superior garden performance.

The 2006 AAS winners include a number of annual flowers and vegetables that should grow well in Minnesota gardens. If you like purple, you're in luck this year -- winning plants include 'Supra Purple' dianthus, a 12 inch tall annual loaded with lacy red-violet flowers; 'Perfume Deep Purple' nicotiana, a compact 20 inch tall annual with fragrant, deep purple, star-shaped flowers; 'Evolution' salvia, a mid-height annual with spikes of rich violet flowers; 'Black Pearl' ornamental pepper, a great garden or container plant with deep purple-black foliage and small, glossy, purple-black fruit; and, believe it or not, 'Purple Haze' carrot, noted for its sweet flavor as well as its startling purple flesh.

Another annual flower winner, 'Diamonte Coral Rose' diascia, loves cool weather and is a great choice for patio containers or hanging baskets. For hot, sunny gardens, check out 'Zowie! Yellow Flame' zinnia, a 24 to 30 inch tall annual with striking red and and yellow bicolor flowers.

The other 2006 AAS vegetable award winners will have you thinking about salsa. 'Carmen' is an Italian-type sweet pepper that matures to a deep red color. 'Mariachi' is a mildly hot chile pepper with loads of cone-shaped fruit that can be used in the yellow or fully mature red stage. 'Delfino' cilantro has the same flavor as other cilantros but it sports attractive finely-cut foliage that looks great in the herb garden or in containers.

Seeds or plants of these award-winning flowers and vegetables are available now in catalogs and at garden centers.

To view many new flower and vegetable varieties, visit these AAS display garden sites in Minnesota:

U of M North Central Research and Outreach Center
1861 Hwy. 169 East
Grand Rapids, MN 55744

U of M West Central Research and Outreach Center
46352 State Highway 329
Morris, MN 56267

U of M Display and Trial Garden
Corner of Gortner and Folwell Avenue
St. Paul, MN 55108

Minnesota Landscape Arboretum
3675 Arboretum Drive
Chaska, MN 55318

Lyndale Park Gardens
4125 E. Lake Harriet Pkwy.
Minneapolis MN 55409

Tiny Reddish Clover Mites Active Now
Jeffrey Hahn, Assist. Extension Entomologist

Clover mite Photo credit: Val Cervenka

Recently, people have been finding tiny reddish brown 'bugs' on the outside of their homes as well as around windows and other sunny areas indoors. This is a type of mite known as a clover mite. They are the size of a pinhead, about 1/30th inch long. If you look very closely you will see that they have a very round body and they lack wings. Clover mites have eight legs with the first pair of legs particularly long. Because of this, people sometimes mistakenly believe that this ‘bug' has antennae. As people try to wipe up these mites, they inevitably discover that if you crush them, they leave a rust colored stain on the surface they were on.

Clover mites spend the summer feeding on grass and clover although they are not considered a pest of plants. It is common for them seek shelter in and around buildings during the fall. However, they seem to be commonly noticed around homes during the spring. They can occur in very large numbers around the foundations of buildings and because of the their small size, it is easy for them to pass through windows. They prefer to be in sun and are most common on the south sides of homes. Despite their abundance, they are not harmful to people or our property (with the exception that if they are crushed they can stain surfaces).

There are a couple of strategies to keep clover mites out of your home. A nonchemical method is to maintain a barrier of clean, bare soil around your home, i.e. free of grass and leaves. Clover mites generally do not cross such a barrier. This barrier should be about 18 - 24 inches wide. If you do have annuals, perennials, or shrubs planted in this zone, have them far enough apart so the clover mites can not easily bridge across this barrier. Landscape rock apparently is not enough of a deterrent to keep clover mites away from buildings.

You can treat the foundation with an insecticide to help keep them from entering your home. Products that contain bifenthrin are the most effective. An example of a product containing this active ingredient is Ortho® Home Defense MAX® Perimeter & Indoor Insect Killer. If you have a hard time finding bifenthrin and it is important to keep them out of your home, consider hiring a professional pest control service to treat the outside of your home.

Once these mites are inside, the best control is physical removal. Use a vacuum cleaner which also helps to minimize crushing them. You can also try a damp cloth but wipe gently so you don't accidentally stain surfaces. Clover mites are a temporary problem that will go away on its own when the weather become warmer.

Be On the Watch For Columbine Sawfly
Jeffrey Hahn, Assist. Extension Entomologist

Cloumbine sawfly Photo credit: Jeff Hahn

If you grow columbine in your garden, watch out for a defoliating insect known as columbine sawfly, Pristophora aquiligae. Sawflies are similar in appearance to caterpillars but grow up to be non-stinging wasps. You can distinguish between them as caterpillars have 2 - 5 pairs of prolegs, fleshy false legs located on their abdomen while sawflies have 6 - 10 pairs of prolegs. Columbine sawflies are green with greenish heads and lack stripes or spots on their body.

Columbine sawfly larvae are active in May feeding on the leaves of columbine. They start along the edge of leaves and feed until only the midveins remain. A badly defoliated plant will look like a stem with thin sticks protruding out. Because of their green color and the fact that they are often on the underside of leaves during the day, it is easy to miss these sawflies until defoliation becomes severe and obvious.

If you have had a problem with columbine sawfly in the past or want to protect your plants against these insects, check your columbine frequently to detect the larvae when they are first active. The younger the sawflies are when you find them, the less damage they have inflicted on your plants. Once you find them, you can determine what the best course of action is. If you are dealing with a small number of sawflies, an easy solution is to handpick them. Just throw them into a bucket of soapy water to be sure they die.

If physical removal isn't practical, there are insecticides that are effective. Insecticidal soap is good low impact product. When using insecticidal soap, it is important to hit the larvae directly with the spray. There isn't any residual activity so any sawflies that walk onto treated leaves later will not be affected by it. Another low impact product that should be effective is spinosad (e.g. Conserve)

There are also any number of residual garden insecticides that would work against sawflies, such as esfenvalerate, bifenthrin, and permethrin. Columbine sawflies are thought to have one generation so after they are gone in June, you should be done with them for the season.

Get the low down on this month's insect pests at Insects
http://www.extension.umn.edu/projects/yardandgarden/EntWeb/Ent.htm

Contributors: Nancy Rose Patrick Weicherding Bob Mugaas

Lawns:
The soil surface temperature is probably warm enough to permit crabgrass seed germination. We're now in the zone for applying pre-emergent crabgrass control products. Sandier soils warm up first and heavier soils lag behind by about a week.

If spring turns cool and wet, a mid-June second application might be necessary.

Now is also an excellent time for broadleaf weed control. Once ambient temperatures get into the mid-80s, it will be too hot to put down herbicides. A still evening is a wonderful time to spritz the weedies. You don't need to spray weeds to the point that they're dripping to get control. Traditional herbicides that are translocated just need to get on some of the foliage.

If you didn't get a late fall fertilizer application done, you still have time for an application this spring. Once the grass has started to grow enough that you've mowed a time or two, you can give you lawn a light does of nitrogen fertilizer. Apply half to three-quarters pounds of nitrogen per thousand square feet. You don't want to force the grass to grow more vigorously and deplete stored carbohydrates.

If rain is not forthcoming in adequate amounts, you may need to water lawns on sandy soil or exposed sites.

Save gas when you mow your lawn by sharpening your mower blade! A dull blade requires 25-30% more energy to mow. Consider buying a spare mower blade so you always have a sharpe one. Blade sharpening may be done at home but some traditional hardware stores, small engine repair shops, among others do the chore.

Change oil and air filters plus the spark plug on your mower for season-long trouble free-mowing.

Trees and Shrubs:

'PJM' rhododendron Photo credit: Beth Jarvis

Be sure to read the label when selecting lawn weed control herbicides. Watch for products that contain dicamba as it can be taken up by tree roots and may injure your trees and shrubs. Mulching a generous area beneath tree canopies reduces the need for weed control under trees.

Don't prune oaks and elms now. About the only woody plants you could prune right now are shrubs that will bloom later in the season.

If Mother Nature turns off the April showers, water your woody plants. They're highly taxed right now because they're putting out leaves and flowers. They shouldn't be stressed for moisture.

All tree wrap should have been removed in April. If your trees are still wrapped with that tape, go unwrap them right now.

It's an ideal time to plant. Garden centers are brimming with great selections. Do your homework before you go. Be sure the plants you select will tolerate the soil type as well as be hardy in your area. Use northern nursery-grown stock or plants from a northern seed source.

Don't forget to look up when deciding where to plant. If utility lines are overhead, pick something short.Right Tree Handbook can provide guidance.

A wealth of information on tree care is at: Urban Forestry Resources site

Other sources of tree selection info include: Trees and Shrubs for Clay Soils, and Click on Trees and Shrubs-Selection http://www.extension.umn.edu/topics.html?topic=5 to review a lot of Extension literature on woody plant selection and care.

Purchasing the biggest tree available is not always the best choice. Smaller transplanted tree establish more quickly and catch up with larger transplanted trees. There is less transplant shock as they've lost fewer roots.

Staking and guying are not recommended unless you're dealing with very large trees or windy sites. If your transplanted tree stands on its own, leave it be. To avoid planting too deeply, be sure to check the depth of the first lateral root and be sure it's not more than 1/2 inch below the soil surface.

Tree fertilization is not recommended at planting time. The latest research indicates threes and shrubs should be fertilized when a soil test indicates a need for fertilizer. Routine, annual fertilizer applications aren't needed.

Foresters and Master Gardeners report there's a great deal of winter injury in evergreens of all kinds this year. It's possibly because we didn't have consistently cold temperatures, or soil moisture either wasn't available due lack of fall watering or because ground was frozen. If you're wondering if your evergreen is now an everbrown, scratch the bark near the tips of the branches. If you see green cambium tissue just under the bark, it's alive. If it's brown all the way to the wood, it's dead. Needles are often not regenerated, so severe damage will warrant replacement. If the stems have green cambium, you might be patient.

Flowers, Fruits and Vegetables:

Pansies, 'Bright Lights' chard, nemesia. Photo credit: Beth Jarvis

Quackgrass in asparagus beds can be killed off now. Use a foam paintbrush--the kind used for trim, to paint a bit of properly diluted glyphosate on the emerging quackgrass. You don't need to drench the grass, just carefully paint the new growth, as this systemic will be absorbed by the weed grass and translocate down to the roots. If you work with a concentrate, be sure to dilute it peer the label. Too much concentrate will simply burn out the leaves and not be absorbed and translocated. Read the label to be sure that the formula you use is straight glyphosate and doesn't include longer-acting herbicides and that it is labeled for use in vegetable gardens.

You can prevent most of the fruit from forming on crabapples and many other trees by using Florel. It must be applied at bloom time, so time is of the essence. (Check with local garden centers for availability.) It's labeled for use on some shade trees trees as well. Examples include: crabapples, apples, maples, oaks and elms. For more information see: http://www.montereylawngarden.com/info/florel.html

Prune out any 2 year old raspberry canes, if you haven't already. If they produced fruit last summer, they won't produce fruit again.

Now's a great time to plant blueberry shrubs. They should be spaced three to four feet apart. Remove flowers for the first two years.

Currants and gooseberries will produce fruit in as little as half-day sun. Most fruit plants need full sun.

Prune out winter-injured, broken stems of fruiting shrubs.

Gardeners in zone 4 can start hardening off home-raised transplants. Gardeners in zone 3 should wait until mid-month. Hardening off means gradually exposing seedlings raised indoors to outdoor conditions. A cold frame is ideal but even a couple of lawn chairs and painters' plastic sheeting will work. Info on building a simple coldframe and a cloche/coldframe is at: http://www.extension.umn.edu/projects/yardandgarden/ygbriefs/h137seasonextenders.html

Tomatoes need warm soils, greater than 60º F., to thrive. Plastic mulch is beneficial as it warms the soil and traps carbon dioxide which escapes through the plant hole and into the canopy--thus improving vegetative growth. And, it reduces weeding. Hold off on applying organic mulch (compost, grass clippings, etc.) until the soil has completely warmed as these mulches keep the soil cool. Read about research into plastic mulches at: http://www.public.iastate.edu/~taber/Extension/Progress%20Rpt%2001/tomearly.pdf Peppers need soil temperatures of 70º F., so hold off on planting them until the very last--late May-early June.

Editorial Notes

Agapanthus, snap- dragons and pansies. Photo credit: Beth Jarvis

It's been said that good fences make good neighbors. Trees can be entirely another matter if neighbors disagree on fruit fall, leaf litter, etc. With that in mind, I'm delighted to report that I've secured the rights to publish a number of articles written by Lorrie Stromme, Hennepin Co. Master Gardener and lawyer. She wrote about litigious neighborhood yard issues as one of the requirements for her Master of Agriculture degree. The articles I'll be reprinting here will cover pruning by utility companies, herbicide drift, hazard trees, nuisance trees and damage to tree. This will start next issue.

Dave Hanson, forester and the guiding light for the Shade Tree Advisor course, will be writing an article some time this summer on growing evergreens in shade. I've asked him to touch on the physiological drawbacks to shade vis a vis incidence of winter injury, among other things.

Dave Bedford, fruit breeder, has agreed to visit with me some rainy day to talk about small fruits for home yards/landscapes.

Please feel free to cut and paste any of the articles for use in your own newsletters. All we ask is that you give our authors credit.

Back issues Yard & Garden Line News are on the Yard & Garden Line home page at www.extension.umn.edu/yardandgarden/

Deb Brown answers gardening questions on Minnesota Public Radio's (MPR) "Midmorning" program on the first Friday of every month at 10 a.m. The program is broadcast on KNOW 91.1 FM, and available state-wide on the MPR news radio stations. (Scroll down for map.)

For plant and insect questions, visit http://www.extension.umn.edu/askmg. Thousands of questions have been answered, so try the search option in the black bar at the top left of the board for the fastest answer.

If you would like to receive an e-mail reminder when the next issue of the Yard & Garden Line News is posted to the web, just send an e-mail to: listserv@lists.umn.edu (note: the second E in listserve is omitted), leave the subject line blank, then in the body of the message, type: sub yglnewslist or to unsubscribe, enter: unsub yglnewslist

Happy gardening!

Beth Jarvis
Yard & Garden Line Project Coordinator


Previous Page
University of Minnesota Extension Service Home Page
In accordance with the Americans with Disabilities Act, this material is available in alternative formats upon request.  Please contact your University of Minnesota county extension office or, outside of Minnesota, contact the Distribution Center at (612) 625-8173.

The University of Minnesota Extension Service is committed to the policy that all persons shall have equal access to its programs, facilities, and employment without regard to race, color, creed, religion, national origin, sex, age, marital status, disability, public assistance status, veteran status, or sexual orientation.